页岩储层中气体多机理耦合渗流研究

页岩储层中有纳米孔、微米孔、微裂隙、人工裂缝等储集空间和运移通道,多尺度的孔隙结构使气体具有扩散、滑脱、达西渗流等多种流动形式。当储层压力、温度、应力改变时,赋存气体的运动状态、孔隙结构会发生改变,使渗流复杂化。利用毛管束模型和平板模型,分别讨论了扩散、吸附、应力解吸对页岩中气体渗流的影响。研究表明:1当温度一定时,在低压小孔隙中,气体的扩散主要是Kudsen扩散;当压力和孔径变大时,则以Fick扩散为主;2在低压小孔隙储层中,扩散对渗流影响不可忽略;但当压力和孔径达到一定值后,可以忽略扩散的影响;3滑脱对气体渗流的影响程度与压力和孔隙尺度有关;4吸附会减小孔隙直径,影响气体渗流,孔隙越小,吸附对渗流的影响越严重;5随有效应力的增加,页岩渗透率降低;页岩中裂缝越多,渗透率降低越显著;气体解吸后页岩的渗透率变大。

Multi-mechanism Coupling Seepage in Shale Gas Reservoir

Shale has nano- and micro-pores, micro fissures and artificial fractures reservoir space and transport channel. The multiscale pore structure has many flow forms, including diffusion, sli- ppage, Darcy flow and so on. When the reservoir pressure and temperature change, the adsorption gas desorp and the pore structure deforms which makes the flow complicated. The paper utilizes single duct model and coupling model to study respectively the effect of diffusion/adsorption and effective stress/desorption on the seepage of shale gas.The research results show that:(1) When reservoir temperature is constant, Kudsen diffusion is the main form in small pore and low pressure and Fick diffusion becomes main form with pore and pressure larger. The Kn is about 10 whne the temperature is 313k and pressure is 0.5MPa for 1nm pores;(2) Diffusion can not be neglected in the conditions of low pressure and small pores, but it is able to neglected when the pressure and pore is a certain large quantity.(3) The effect of slippage is related to the pressure and pore, but it is an important factor all the time.(4) The adsorption of gas decreases the pore diameter and has a more notable effect in small pore.(5) The permeability decreases with the effective stress increasing and the more cracks, the lower the permeability. The permeability become larger when the adsorption gas begins to desorb.